Strengthening mechanism of hot rolled Ti and Nb microalloyed HSLA steels containing Mo and W with various coiling temperature

The effect of Mo- and W-addition on the precipitation hardening of Ti- and Nb-microalloyed high-strength low-alloy steels was investigated. The variation in simulated hot-coiling temperature caused a significant difference in strength, which is attributed mainly to different precipitation-hardening behavior. Among the four alloys with different combination of the microalloying elements: Ti-Mo, Nb-Mo, Ti-W, and Nb-W, the steel with Nb-Mo turned out to be the most effective in precipitation hardening. The strengthening mechanism was discussed based on the microstructural evolution observed by electron microscopy and the theoretical considerations combining the different hardening models.